The purpose of this proposal is to identify and characterize bacterial surface groups that react in a selective way with the Fc regions of a variety of different immunoglobulin classes and subclasses from various mammals. In particular, we propose to study the number of functionally distinct Fc receptors associated with group A streptococci. To date, two functionally distinct but antigenically related Fc receptors have been found associated with one group A streptococcal strain. Future studies will be directed toward fully characterizing these receptors. This will include studies of their physicochemical composition and cloning of the gene or genes coding for these proteins. In addition, the biological activities of these molecules for these Fc receptors will be studied. These studies will include measurement of the ability of Fc receptors to mediate complement activation in serum and measurement of their mitogenic potential for peripheral blood lymphocytes. The role of bacterial Fc receptors in the disease course and post-infection sequelae of certain infections will be explored as suitable reagents become available.